This invention relates to gas turbine combustors, and particularly to a fracture resistant support structure for a so-called xe2x80x9chula sealxe2x80x9d between a combustion liner and a transition piece. The support structure is placed between the hula seal and combustion liner.
Current combustion liner cooling sleeves are attached at their forward ends to the radially inner combustor liner with a circumferential fillet weld (either intermittent or continuous). For purposes of this discussion, the xe2x80x9caftxe2x80x9d end is that which is closer to the exit face of the liner, while the xe2x80x9cforwardxe2x80x9d end is that which is closer to the inlet of the liner. Generally, the liner runs hotter than the outer sleeve by 300-500xc2x0F., because the liner is exposed directly to the hot combustion gases. More specifically, the liner temperature is typically in the 1200-1400xc2x0 F. range, whereas the outer sleeve temperature is typically in the range of 700-900xc2x0 F. If the initial radial gap between the sleeve and liner is set to zero, then the liner will expand more than the outer sleeve, and will therefore create compressive radial stresses at the interface, and tensile hoop stresses in the outer sleeve. The resulting thermally induced deformations cause hoop extension such that the outer sleeve diameter increases to the extent that the sleeve is permanently deformed. During the cooling cycle, however, the liner contracts but the outer sleeve cannot return to its original diameter due to the permanently set deformation. The inability of the outer sleeve to recover its original shape creates a radial gap which acts as a crack opening displacement, impinging on the fillet weld. This crack opening displacement may increase the stress intensity factor to the critical stress intensity factor (KIC) in order to drive the crack into the weld.
In the present invention, the outer sleeve is made slightly oversized to produce a radial gap between the liner and the outer sleeve at ambient temperature. The gap is calculated by considering the operating temperatures of both components and their respective thermal expansion coefficients. The calculated value is the value that will create no thermal mismatch stresses. Once the gap is determined, the outer sleeve can be formed with the appropriate diameter. The aft end of the outer sleeve is swaged inwards an amount equal to the gap value to insure that the edge of the outer sleeve touches the liner. After welding prep is applied, the outer sleeve is welded over the liner. Because of the swaged end, the crack tip that impinges on the fillet weld is no longer infinitely sharp. Rather, a blunt crack tip is provided that reduces the stress intensity factor in the weld, and thus reduces the propensity for cracking.
To further reduce the crack driving energy, the outer sleeve may be separated into multiple segments at the welded end. Each segment is welded with an independent fillet weld so that the fracture energy in each segment is limited, and the segments are flexible during thermal growth. These segments are positioned with respect to axial slots in the liner and the in respective cooling holes in the outer sleeve.
In one embodiment, the axial channels in the liner are completely covered by the outer sleeve. The air inlet holes in the outer sleeve are placed over a circumferential channel which acts as a plenum and feeds air into the axial channels.
In a second embodiment, the axial channels extend beyond the length of the outer sleeve. The exposed length of the axial channels provides air inlet locations, thus replacing the inlet holes of the previous design.
The number or location of the segments can be independent of the number and location of the axial channels and the location of air inlet holes.
Accordingly, in its broader aspects, the present invention relates to a combustion liner and outer cooling sleeve assembly for a turbine combustor comprising a substantially cylindrical combustion liner having a forward end and an aft end; and a substantially cylindrical outer cooling sleeve surrounding at least an axial portion of the combustion liner; wherein the outer cooling sleeve is secured to the combustion liner by a weld at an end of the outer cooling sleeve, with a predetermined radial gap between the combustion liner and the outer cooling sleeve extending at least partially about the combustion liner, the radial gap determined by respective operating temperatures and thermal expansion coefficients of the combustion liner and the outer cooling sleeve.
In another aspect, the invention relates to a combustion liner and cooling sleeve assembly for a turbine combustor comprising a substantially cylindrical combustion liner; and a substantially cylindrical cooling sleeve surrounding at least an axial portion of the combustion liner; wherein the outer cooling sleeve is secured to the combustion liner by a weld at one end of the outer cooling sleeve, with a predetermined radial gap between the combustion liner and the cooling sleeve; wherein the end is circumferentially divided into segments and wherein the weld is continuous in each segment; and further wherein the end is swaged radially inwardly an amount equal to the radial gap such that the end engages an outer surface of the combustion liner.
In still another aspect, the invention provides a method of reducing crack propensity in a substantially cylindrical combustion liner and substantially cylindrical outer cooling sleeve assembly where one end of the outer cooling sleeve is welded to the combustion liner, the method comprising a) determining a radial gap between the combination liner and the outer cooling sleeve as a function of operating temperatures and thermal expansion coefficients of the combustion liner and the cooling sleeve; b) forming the outer cooling sleeve with a diameter sufficient to provide the radial gap; c) swaging the end of the outer cooling sleeve to bring the end into engagement with the combustion liner; and d) welding the outer cooling sleeve to the combustion liner about the end.